A heart of a mammalian animal is a hollow muscular organ having left and right atria and left and right ventricles, each provided with its own one-way valve. A natural heart includes aortic, mitral (or bicuspid), tricuspid and pulmonary valves, and each valve has one-way leaflets to control a directional flow of blood through the heart. The valves are each supported by an annulus that comprises a dense fibrous ring attached either directly or indirectly to the atrial or ventricular muscle fibers. Over time, the heart (e.g., the valve) may become diseased or damaged. To repair the heart, the valve may undergo a valve replacement operation. In one operation, the damaged leaflets of the valve are excised, and the annulus is sculpted to receive a replacement valve, such as a prosthetic heart valve. Although various types and configurations of prosthetic heart valves for replacing diseased natural human heart valves are known, such valves conventionally comprise a valve and a sewing ring supporting valve leaflets and commissure posts.
Bio-prosthetic valves can be formed from an intact, multi-leaflet porcine (pig) heart valve, or by shaping a plurality of individual leaflets out of bovine (cow) pericardial tissue and combining the leaflets to form the valve. The pericardium is a sac around the heart of vertebrate animals, and bovine pericardium is commonly used to make individual leaflets for prosthetic heart valves.
Steps in a typical commercial process for preparing pericardial tissue for heart valve leaflets include first obtaining a fresh pericardial sac, and then cutting the sac open along predetermined anatomical landmarks. The sac is then flattened and typically cleaned of excess fat and other impurities. After trimming obviously unusable areas, a window or patch of tissue is fixed, typically by immersing in an aldehyde to cross-link the tissue. Rough edges of the tissue window are removed and the tissue bio-sorted to result in a tissue section. The process of bio-sorting involves visually inspecting the window for unusable areas, and trimming the section therefrom.
The section is then placed flat on a platform for thickness measurement using a contact indicator. The thickness is measured by moving the section around the platform while a spindle of the indicator moves up-and-down at various points. The thickness at each point is displayed and recorded. After sorting the measured sections by thickness, leaflets are die cut from the sections, with thinner leaflets generally being used for smaller valves, and thicker leaflets being used for larger valves. Of course, this process is relatively time-consuming and the quality of the final leaflets is dependent at several steps on the skill of the technician. Moreover, the number of leaflets obtained from each sac is inconsistent, and subject to some inefficiency from the manual selection process.
To help speed up the process of identifying areas of similar thickness in the pericardial sections, a system and method to topographically map the sheet into similar thickness zones for later use is disclosed in U.S. Pat. No. 6,378,221 to Ekholm, Jr., et al. The system includes a three-axis programmable controller for manipulating a bio-material workpiece with respect to a thickness measurement head which has a plurality of thickness gauges or sensors for simultaneous measurement of a plurality of points, with the sensors being adapted to contact the sheet or not. A marking head may be provided for marking the zones or otherwise indicating the thickness in different areas. The measured or marked sheet is then removed from the system for further processing into leaflets.
Despite advancements in assessing bioprosthetic tissue for heart valve leaflets and other uses, there remains a need for a more accurate and efficient process. Additionally, the need is more important for thinner leaflets, such as used in smaller surgical valves or in compressible/expandable valves for percutaneous or minimally-invasive surgeries, since the presence of uneven or mismatched leaflets is relatively more detrimental to proper valve functioning.